|
|
Crystallization of binary polylactide blends and their morphology
Debnáriková, Michaela ; Poláček, Petr (referee) ; Bálková, Radka (advisor)
Master thesis deals with the influence of polyvinylacetate, polycaprolactone, poly(butylene-adipate-co-terephtalate) and talc, ethylenevinylacetate, polyethylene glycol and monosodium citrate on the flow properties, mechanical properties and crystallization ability of PLA. The flow properties were studied using the melt flow index and mechanical properties were studied using a tensile test. The crystallinity was studied by differential scanning calorimetry and on a polarization optical microscope equipped with hot stage. Isothermal crystallization was performed at 95 and 105 °C for 3 h and non-isothermal crystallization was performed with a calorimeter at two cooling rates (1 and 10 °C/min). Upon the isothermal crystallization at 95 °C, the formation of denser crystalline structure was observed and the content of crystalline phase increased in most of the samples. The formation of spherulitic structure was observed at 105 °C in samples with 30 % PVAc, 30 % EVA and PEG. Reducing the cooling rate to 1 °C/min at non-isothermal crystallization had nearly no effect on the crystallization process of the most samples; the content of crystalline phase increased in the samples containing PBAT and PEG, which revealed double melting peak during subsequent heating. The crystalline fraction was the most significantly affected by the addition of PEG. All added polymers except PVAc affected the mechanical properties; PBAT, PCL, EVA and PEG increased the strain and decreased the strength and modulus of elasticity. The samples containing monosodium citrate showed unsatisfactory mechanical properties and could not be measured. The samples containing higher concentration of EVA copolymer showed the phase separation.
|
|
|
Effect of different type and crosslinking density of polyethylene glycol hydrogels on transport and sorption properties
Janáková, Kristýna ; Pekař, Miloslav (referee) ; Krouská, Jitka (advisor)
The main goal of this work was to study the transport and sorption properties of polyethylene glycol (PEG) hydrogels with different types and densities of cross-linking. Before characterizing these properties it was necessary to optimize the preparation of selected hydrogels including the study of mechanical properties using rheological measurements. A significant part of the work, therefore, consists of the optimization of PEGDA-thiol hydrogels created from 4-arm polyethylene glycol-thiol (PEG-4SH) and polyethylene glycol diacrylate PEGDA by step-growth polymerization. To compare the transport and sorption properties of another type of crosslinking, PEGDA hydrogels were prepared using radical polymerization. In the transport experiments, the sorption and desorption of the Rhodamine 6G dye were monitored using free diffusion. Molecular absorption spectrometry (UV/VIS) was used to characterize the course of these experiments. The structure of these gels was compared using scanning electron microscopy.
|
|
|
Crystallization of binary polylactide blends and their morphology
Debnáriková, Michaela ; Poláček, Petr (referee) ; Bálková, Radka (advisor)
Master thesis deals with the influence of polyvinylacetate, polycaprolactone, poly(butylene-adipate-co-terephtalate) and talc, ethylenevinylacetate, polyethylene glycol and monosodium citrate on the flow properties, mechanical properties and crystallization ability of PLA. The flow properties were studied using the melt flow index and mechanical properties were studied using a tensile test. The crystallinity was studied by differential scanning calorimetry and on a polarization optical microscope equipped with hot stage. Isothermal crystallization was performed at 95 and 105 °C for 3 h and non-isothermal crystallization was performed with a calorimeter at two cooling rates (1 and 10 °C/min). Upon the isothermal crystallization at 95 °C, the formation of denser crystalline structure was observed and the content of crystalline phase increased in most of the samples. The formation of spherulitic structure was observed at 105 °C in samples with 30 % PVAc, 30 % EVA and PEG. Reducing the cooling rate to 1 °C/min at non-isothermal crystallization had nearly no effect on the crystallization process of the most samples; the content of crystalline phase increased in the samples containing PBAT and PEG, which revealed double melting peak during subsequent heating. The crystalline fraction was the most significantly affected by the addition of PEG. All added polymers except PVAc affected the mechanical properties; PBAT, PCL, EVA and PEG increased the strain and decreased the strength and modulus of elasticity. The samples containing monosodium citrate showed unsatisfactory mechanical properties and could not be measured. The samples containing higher concentration of EVA copolymer showed the phase separation.
|
|
| |
|
| |
|
| |
guest ::
